Ketones are technically versatile and valuable products and are known to be prepared e.g. via the oxidation of secondary alcohols, the hydrogenation of unsaturated ketones, the decarboxylation of carboxylic acids and the hydration of non-terminal alkynes. Most of these reactions have in common that they use starting materials which as such are already valuable compounds, and are often prepared via processes which are conducted under stringent reaction conditions and/or necessitate laborious product isolation procedures.
A considerable improvement in the preparation of ketones would be achieved by employing a relatively cheap or more readily available feedstock or starting material. Such a process is known from Japanese applications 73-34728 and 74-48407 and relates to the reaction in the gas phase of an at least C.sub.5 -conjugated diolefin with water in the presence of an acidic catalyst and employing a water to conjugated diene weight ratio in the range of from 0.05:1 to 50:1. From the examples it appears that the yield of ketone is strongly dependent on and proportional to the water to diene ratio, a water to diene weight ratio of 41.5:1 still only resulting in a 48.7% yield of ketone based on isoprene supplied, while with a 2:1 weight ratio said yield is only 16%. The apparent requirement of such a large excess of water for a process which is conducted in the gas phase makes this process very unattractive from this energy consumption point of view. Not only does the evaporation of water require a lot of energy, but so will also the recovery of the ketone from the very dilute mixture. A further disadvantage of said process that it is restricted to conjugated diene having at least an isoprene configuration. Hence it can be concluded that there is considerable need for improvement in the preparation of ketones.
The problem underlying the present invention is developing a process for the preparation of ketones which does not have one or more of the disadvantages mentioned hereinbefore.
As a result of extensive research and experimentation, it has been found that ketones may be prepared from the reaction of conjugated diolefins with water in the presence of a catalyst system based on group VIII metals.